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LNK408LG Datasheet(PDF) 7 Page - Power Integrations, Inc. |
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LNK408LG Datasheet(HTML) 7 Page - Power Integrations, Inc. |
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Rev. D 08/11 7 LNK403-409/413-419 www.powerint.com 7 W High Power Factor Non-Dimmable LED Driver Design Example with Enhanced Line Regulation The circuit schematic in Figure 7 shows a high power-factor LED driver based on a LNK413EG from the LinkSwitch-PH family of devices. It was optimized to drive an LED string at a voltage of 21 V with a constant current of 0.33 A, ideal for PAR20/PAR30 lamp retro-fit applications. The design operates over the universal input voltage range of 90 VAC to 265 VAC and is a non-dimming application. A non-dimming application has tighter output current variation with changes in the line voltage than a dimming application. It’s key to note that, although not specified for dimming, no circuit damage will result if the end user does operate the design with a phase controlled dimmer. Circuit Description Input Stage Fuse F1 provides protection from component failures while RV1 provides a clamp during differential line surges, keeping the peak drain voltage of U1 below the 725 V rating of the internal power FET. Bridge rectifier BR1 rectifies the AC line voltage. EMI filtering is provided by L1-L3, C2 together with the safety rated Y class capacitor (C7) that bridges the safety isolation barrier between primary and secondary. Resistor R2 and R3 act to damp any resonances formed between L1, L2, C2 and the AC line impedance. A small bulk capacitor (C3) is required to provide a low impedance source for the primary switching current. The maximum value of C2 and C3 is limited in order to maintain a power factor of greater than 0.9. LinkSwitch-PH Primary To provide peak line voltage information to U1 the incoming rectified AC peak charges C8 via D6. This is then fed into the VOLTAGE MONITOR pin of U1 as a current via R4, R7 and R8. The VOLTAGE MONITOR pin current and the FEEDBACK pin current are used internally to control the average output LED current. The combined value of R4, R7 and R8 (3.909 MW) and R11, R12 (1.402 MW) connected to the VOLTAGE MONITOR pin provides excellent line regulation over the entire 90 VAC to 265 VAC input range. The VOLTAGE MONITOR pin current is also used by the device to set the line input overvoltage and undervoltage protection thresholds. Diode D1 and VR1 clamp the drain voltage to a safe level due to the effects of leakage inductance. A Zener clamp was selected for lowest component count and highest efficiency. Diode D5 is necessary to prevent reverse current from flowing through U1 during the period when the AC input voltage is lower than the reflected output voltage (V OR). A space efficient RM6 core was selected for this design. The RM core geometry helps minimizes audible noise but requires the use of flying leads to meet safety spacing requirements. Diode D3, C6, R5, R9 and R18 create the primary bias supply from an auxiliary winding on the transformer. Resistor R5 provides filtering of leakage inductance generated voltage spikes to improve tracking of the bias and output voltages. It also forms a pole with C6 at ~100 Hz. Resistors R9 and R18 act as a small load to ensure that the bias voltage collapses during output short-circuit when U1 enters auto-restart operation to protect the supply. Output overvoltage and load disconnection protection is provided by D8, C14, R24, VR3, C15, R23 and Q2. Should the output LED load become disconnected the output voltage will rise causing an associated rise in the bias winding voltage across C14. Once this exceeds the voltage rating of VR3, Q2 turns on pulling down the FEEDBACK pin of U1 and initiating auto-restart operation. Once in auto-restart the low duty cycle of operation (~3%) together with the small pre-load on the output prevents the output voltage rising to a high level. Once the output load is reconnected normal operation resumes. Capacitor C12 provides local decoupling for the BYPASS pin of U1 which is the supply pin for the internal controller. During Figure 8. Schematic of an Isolated, Non-Dimmable, High Power Factor, Universal Input, 7 W LED Driver. PI-5991-101210 D S BP V R FB CONTROL FL2 T1 RM6 FL1 1 FL3 6 2 R4 2 M Ω 1% R2 1 k Ω L1 1000 µH L3 1000 µH L2 1000 µH R3 1 k Ω R7 1 M Ω 1% R8 909 k Ω 1% R11 1.0 M Ω 1% R12 402 k Ω 1% R19 24.9 k Ω 1% R15 150 k Ω R6 20 k Ω 21 V, 330 mA 90 - 265 VAC RTN L N R9 10 k Ω R18 10 k Ω R5 75 Ω R10 3 k Ω R23 1 k Ω D6 DL4007 D1 UF4007 D4 1N4148 VR3 ZMM5259B-7 39 V Q2 MMBT3904 D8 BAV21WS-7-F D3 DL4936 D2 MBRS4201T3G D5 ES1D VR1 P6KE200A R24 10 k Ω BR1 DF06S-E3/45 600 V F1 3.15 A RV1 275 VAC C5 150 µF 35 V C7 2.2 nF 250 VAC C4 150 µF 35 V C12 10 µF 10 V C14 1 µF 50 V C15 100 nF 50 V C6 22 µF 50 V LinkSwitch-PH U1 LNK413EG C8 1 µF 400 V C2 22 nF 275 VAC C3 100 nF 400 V |
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